Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. In many situations, the underground utilities can be buried in a trench which is then back-filled. Although useful in areas of new construction, the burial of utilities in a trench has certain disadvantages. In areas supporting existing construction, a trench can cause serious disturbance to structures or roadways. Further, there is a high probability that digging a trench may damage previously buried utilities, and that structures or roadways disturbed by digging the trench are rarely restored to their original condition. Also, an open trench may pose a danger of injury to workers and passersby.
The general technique of boring a horizontal underground hole has recently been developed in order to overcome the disadvantages described above, as well as others unaddressed when employing conventional trenching techniques. In accordance with such a horizontal boring technique, also known as horizontal directional drilling (HDD) or trenchless underground boring, a boring system is situated on the ground surface and drills a hole into the ground at an oblique angle with respect to the ground surface.
The HDD process includes a pilot hole-boring step. In this step a bore hole is created that extends underground—generally horizontally or generally parallel to the surface of the earth—starting at a launch point and ending at a termination point. The bore hole is created by positioning a boring machine to rotate and push a drill string through the ground. A drill bit is attached to the leading end of the drill string. The drill string is created by connecting individual drill rods together end-to-end from a supply of drill rods stored on the boring machine. The connection between the rods is made up, and subsequently broken in a later step, by the boring machine.
A drilling fluid can be flowed through the drill string, over the boring tool, and back up the borehole in order to remove cuttings and dirt. After the boring tool reaches a desired depth, the tool is then directed along a substantially horizontal path to create a horizontal borehole. After the desired length of borehole has been obtained, the tool is then directed upwards to break through to the earth's surface. A reamer is then attached to the drill string which is pulled back through the borehole, thus reaming out the borehole to a larger diameter. It is common to attach a utility line or other conduit to the reaming tool so that it is dragged through the borehole along with the reamer.
Another technique associated with horizontal directional drilling, often referred to as push reaming, involves attaching a reamer to the drill string at the entry side of a borehole after the boring tool has exited at the exit side of the borehole. The reamer is then pushed through the borehole while the drill rods being advanced out of the exit side of the borehole are individually disconnected at the exit location of the borehole. A push reaming technique is sometimes used because it advantageously provides for the recycling of the drilling fluid. The level of direct operator interaction with the drill string, such as is required to disconnect drill rods at the exit location of the borehole, is much greater than that associated with traditional horizontal directional drilling techniques.